1. Field of the Invention
The invention relates to the regulation of pressurized air in self-contained underwater breathing apparatus, and more particularly to improving the operation of a second stage demand-type regulator by including an adjustable venturi mechanism.
2. Prior Art
Breathing apparatus of the type used in underwater diving systems commonly employ a two-stage regulator arrangement for controlling the flow of air from a pressurized air supply tank. A first stage regulator is mounted directly to the air supply tank and is connected to a second stage regulator by a length of flexible hose. The second stage regulator usually includes a lightweight housing with a mouthpiece capable of being comfortably retained in the user's mouth.
The housing defines a breathing chamber through which the user inhales and exhales air with the aid of a flexible diaphragm in the housing. On a breathing chamber side, the diaphragm communicates with an air inlet valve as well as with the air in the breathing chamber. On the opposite side the diaphragm is exposed to ambient pressure. When the user inhales, the pressure in the breathing chamber falls below ambient pressure. The diaphragm collapses inwardly toward the breathing chamber, opening the air inlet valve and admitting pressurized air into the breathing chamber. When the user exhales, increased pressure in the breathing chamber deflects the diaphragm outwardly relative to the breathing chamber and closes the valve. A check valve arrangement or the like in a wall of the breathing chamber permits air to be exhausted from the housing as the user continues to exhale. The mechanism advantageously is set up so that the user is not required to make an effort to inhale or to exhale that is substantially greater than when breathing in the open air, which effort normally is only minimal.
The opposite may be the case due to the tendency of known regulators to "free flow." Free flow conditions are different than the conditions of normal breathing. Free flowing is caused by the venturi effect, wherein the stream of inhaled air passing through the mouthpiece from the breathing chamber produces a sustained, relatively low pressure in the breathing chamber apart from (or in addition to) the pressure drop caused by any effort exerted by the user to inhale. This low pressure in the breathing chamber affects operation of the diaphragm, i.e., the low pressure keeps the diaphragm collapsed. The inlet valve remains open and continues to admit air into the breathing chamber. Once the flow has begun, the venturi effect can continue the delivery of air after the user's demand to inhale through the demand regulator ceases.
A slight assist from the venturi effect can be desirable because it enhances the inhalation characteristics of the regulator. On the other hand, extended breathing with a regulator that has a considerable tendency to free flow can be annoying. It is also disconcerting for a beginner due to the departure from normal breathing conditions.
Methods and apparatus have been suggested by the prior art for adjusting a demand regulator's tendency to free flow. U.S. Pat. No. 4,041,977--Matsuno; 4,147,176--Christianson; 4,616,645--Pedersen et al.; and 4,796,618--Garraffa, disclose apparatus adapted for regulating the flow of air through a demand regulator. Although providing generally satisfactory operation, many of the prior art demand regulators suffer from inherent problems. In particular, many of the prior art demand regulators do not provide for an easily adjustable air flow so that both the experienced and inexperienced diver may easily and comfortably control venturi related air flow effects according to their preferences and in varying situations.